Recently photohardenable layers have been used as reproduction materials for many purposes. In the production of images using such materials, differences in the properties of the exposed and unexposed areas of the photohardenable layer are used, e.g., differences in solubility, differences in the point of softening or tackiness, variations in adhesion, etc.
Primarily such materials have gained great practical significance where the solubility of the exposed areas is greatly decreased. After imagewise exposure the unexposed areas of the layer can be removed with a suitable solvent, while the exposed areas, due to their decreased solubility against the solvent, are resistant to development. According to this process, after liquid development, a negative relief image of the original is obtained. The development step generally is carried out so that, first, the unexposed parts of the photohardenable layer swell under the influence of the solution. Subsequently, the swelled areas are removed either by the liquid developer, or by a subsequent washing or spraying process. Either organic solvents, such as e.g., chlorinated hydrocarbons, or aqueous alkali solutions are used as the developing liquid.
It is of particular importance to the quality of a developed material that the solubility differences between the exposed and unexposed areas be as large as possible, i.e., that the material has a broad processing range. For example, if the solubility differences between exposed and unexposed areas are very small, there is the danger that during the development step and exposed areas may have already started to dissolve before the building up of the relief image is finished. This can lead to a poorly formed relief, thin layers, or a decrease in sharpness of the image.
A further disadvantage of reproduction materials with a narrow processing range is that it is necessary to closely control the development time as well as the activity and temperature of the developer. Such close control results in considerable added expense in terms of machinery.
The processing range of a photohardenable material depends on its composition and is substantially determined by the binder used and the photohardenable ingredient of the layer. An additional factor which influences the processing range is the developer system used. Therefore, in actual practice, it is always necessary to make substantial compromises between the optimal composition of the photohardenable layer and, thus, the attainable quality of the image, on the one hand, and a still representative processing speed and processing range, on the other hand.
Therefore, it is an object of this invention to provide a process which makes it possible to broaden in a simple manner the processing range of negatively functioning photohardenable materials which are processed by liquid development without interfering with the composition of the material and the developer system.